Tailorable Morphology of Core-Shell Nanofibers with Surface Wrinkles for Enhanced Gas-Sensing Properties

One-dimensional core-shell nanostructures have attracted considerable attention because of their excellent carrier transport characteristics between core and shell layers. In this work, we report the preparation of surface-wrinkled In₂O₃@ZnO core-shell nanofibers (IZO CSNFs) in a facile way, where the as-spun polyacrylonitrile/indium nitrate (PAN/In(NO₃)₃) nano fibers are used as scaffolds directly in subsequent atomic layer deposition process. The thermal decomposition of the PAN can lead to the formation of the wrinkled ZnO shells. Especially, an evolvement has been observed from solid to hollow IZO CSNFs with the increase of shell thickness, where the ZnO thick shell is robust enough and may act as another type of scaffold to tailor their morphologies. Considering the different carrier transport features in various atmospheres, the IZO-x (x is the number of ALD cycles) sensors exhibit a clear shell thickness dependence on their gas-sensing properties compared to the cases of pure In₂O₃ and ZnO NFs. Furthermore, the IZO-50 CSNF-based sensor shows the highest response to NO₂ (R_g/R_a = 78.6 at 50 ppm, R_a: resistance in air; R_g: resistance in target gas) at a low operating temperature of 200 ºC. Meanwhile, the sensor based on IZO-300 CSNFs presents the superior ethanol sensing response (R_a/R_g = 29.3 at 100 ppm) at 320 ºC. Possible gas-sensing mechanisms of these surface-wrinkled IZO CSNFs are discussed in detail.